This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. Receptor Tyrosine Kinases (RTKs) are large single span membrane proteins that mediate many important cellular functions. While much progress has been made in the understanding of the soluble domains of the receptors, a picture of the whole receptor, including the membrane spanning helix. This lack in information is limiting for a full mechanstic understanding of the signal transduction mechanism(s) of this important class of membrane proteins.